Variable pulley transmissions for transferring torque from an input shaft to an output shaft have been used for some time. The variable pulley transmission usually comprises a first pulley mounted on the input shaft, the pulley having at least one flange axially movable relative to its other flange to change the effective pulley diameter. A second, similarly adjustable pulley is mounted on the output shaft, and the pulleys are intercoupled by a flexible belt to transfer torque therebetween. As the effective diameter of one pulley is changed, and simultaneously the effective diameter of the other pulley is changed in the opposite direction, the drive ratio between the input and output shafts is adjusted in a smooth, continuous manner.
For several decades automotive engineers have recognized that the maximum operating efficiency of the engine could be achieved if the transmission could be controlled by adjusting to different loads and speed ratios such that the engine is maintained at its maximum efficiency point. This is not possible with a conventional geared transmission in which the drive ratio is adjusted in discrete steps, rather than continuously. Accordingly, efforts have been directed to the use of a continuously variable transmission of the type described above. This has resulted in the production and marketing in Europe of the Daf passenger car, using a flexible rubber belt in such a continuously variable transmission (CVT). Flexible rubber belts in such use are subject to wear by reason of the torque they must handle, and operate under severe temperature, vibration and other adverse conditions. To improve belt life, efforts have been made to produce a flexible metal belt, and some of these efforts are described in the patent literature.
One type of metal belt which has been described is composed of a central carrier or indexing strand composed of a plurality of nested, endless, metal bands on which are threaded a plurality of generally trapezoidal or V-shaped (when viewed from the front ) metal load or drive blocks, the blocks being longitudinally slidable along the carrier or indexing strand during operation. Because the individual blocks are in compression as they transfer torque between the pulleys, this type of flexible belt is frequently termed a "push" belt. It is relatively expensive to manufacture because the endless metal bands must be matched for their nested assembly, the load blocks must be stamped and finished, then the blocks must be assembled onto the strand of nested bands. As example of this type of push belt is described in U.S. Pat. No. 3,720,113.
Another type of flexible metal belt uses an endless chain as the carrier or indexing strand in lieu of the more expensive nested endless band array. A belt in which the carrier or indexing strand is a chain is generally termed a "chain-belt." The chain links sets are connected by cylindrical pins, or other suitable pivot means. The drive or load blocks are generally trapezoidal or V-shaped and are positioned between a pair of consecutive pivot members. The drive or load blocks in a chain-belt have little, if any, longitudinal movement with respect to the chain and the pivot members. This type of chain-belt is termed a "pull" belt, and is much less expensive to manufacture than the "push" belt described before because the chain links and load blocks are stamped from sheet metal and the parts are assembled by automatic machinery. There is no need to match the band lengths required for nesting the enless bands for the push type belt. Also installation and replacement of a pull belt is much simpler than the push type belt. An example of a pull type chain-belt is described in U.S. Pat. No. 4,313,730. The push belt is a continuous loop and requires disassembly and re-assembly of the pulleys when installing or replacing a belt; the pull belt can be manufactured in a finite length, wrapped around the pulleys and the ends connected to form the continuous loop.
As shown in the latter patent, each load block of an assembly defines a central window through which links pass, i.e., the load blocks surround the sets of links. As the torque requirements are increased, wider chain is required, which also requires wider load blocks. Because of the loading of the block, various stresses are introduced into the blocks, at times leading to their failure. Thus it has been suggested to provide multiple window blocks with a sub-set of links passing therethrough, the sub-sets being joined by a common pivot means.
In the development of the chain-belt, various types of pivot or joint means, i.e., those parts which pivotably interconnect sets of links, have been suggested. These include round pins and rocker joints, the latter comprising what is termed a pin and a rocker. In some cases, a pin and a rocker differ in cross-section and in other cases they have the same cross-section. Usually, one of the two is of a different length than the other and the longer part extends exteriorly of the side links of a chain. To retain the links in the assembly it has been customary to peen over the ends of the part. The use of a generally C-shaped clip to retain the chain parts in the assembly has been suggested. One form of such a clip spans the chain from side to side with clip ends engaging the ends of the pivot means. Another form of a C-shaped clip is one which is received in a groove in the pivot member abutting a side link of the chain. For this type, two such clips are required for each joint member. Such a clip is illustrated in U.S. Pat. No. 1,488,710 issued Apr. 1, 1924. The latter is described with reference to a chain and not a chain-belt, i.e., an assembly of a chain and load blocks, as will be described herein.
Theoretically, in a chain-belt, when the belt enters a pulley, the blocks are aligned radially. However, in actual practice, the load blocks have a tendency to tilt with respect to the carrier, i.e., the chain and the edges of the windows "dig" into and damage the chain links. For some unexplained reason, damage to the links' lower surfaces is more severe than damage to the links' upper surfaces. Nevertheless, severe damage to the links can cause premature failure of the belt. The amount of damage of this nature can be materially reduced by the invention herein to be described.